A police officer and soldiers on security duty inside the Galerie de la Reine in Brussels on Sunday.
Photograph: Stephanie Lecocq/EPA

Belgian armed police have mounted raids across the country, arresting at least six suspects after the prime minister announced another day of lockdown in the capital for fear a new, Paris-style mass attack may be imminent.

Armed police mounted searches in several parts of the capital on Sunday evening and cordoned off areas close to the main tourist attraction, the Renaissance Grand Place, around the town hall. The public broadcaster said there were also raids near Liege in the east and Charleroi, south of Brussels. Helicopters could be heard flying over the capital. Police evacuated restaurants in the centre, blocked off roads and issued requests to residents to stay away from windows.

Shortly before midnight, the public broadcaster, announcing at least six arrests, said the operations had concluded.

It does not appear that Salah Abdelslam, the alleged logistician behind the Paris Attacks who is on the run, was among those detained. Other raids were conducted in Molenbeek, a borough of Brussels where Abdelslam lived, and in Charleroi, where one man was taken into custody. A further operation took place in Liege, 120 km (75 miles) east of Brussels.

Europe’s de facto capital faces an unprecedented security lockdown this week after Belgian authorities imposed a slew of safety-first measures to prevent a “serious and imminent” terrorist attack. Schools, universities and kindergartens will be shut on Monday and the metro, shuttered all weekend, will remain closed as counter-terrorist forces intensify their search for a network of Islamist militants involved in the Paris attacks.

Charles Michel, the Belgian prime minister, told a tense press conference on Sunday afternoon: “We still fear attacks here like those that occurred in Paris, involving several individuals striking simultaneously in several places,” adding that there were “indications” that transport systems, commercial centres, shopping streets and busy places were targets.

“We realise that these measures will complicate economic and professional life … and we are doing everything we can to return to normality as soon as possible,” Michel told reporters.

He spoke after the government raised the threat level in and around Brussels to four – the highest level – and deployed hundreds of troops to supplement armed local police.

EU institutions will remain open, although with extra security checks, a spokesman said. Officials are expected to issue fresh guidance on further measures, a spokesman for the European commission said.

Officials have also confirmed that nursery schools will be closed on Monday, adding to the chaos that many are predicting for the Belgian capital as the working week begins.

The minister of education, Joëlle Milquet, said the closure of all educational institutions could be extended beyond 24 hours. “You do not mess around with the security of children and students ... This was the only sure measure of protection which we could take,” she told local TV networks.

Shops and restaurants remained shut during the day on Sunday in Brussels with few people in the streets. Museums and cinemas were also closed. Prospects for Britain’s Davis Cup tennis clash with Belgium going ahead on Friday appeared slim.

“We’ve never had this kind of terrorist threat here before. It’s very unexpected, almost surreal,” said Alinka Le Comte, 26, a shop assistant in the centre of the city.

Earlier in the day tourists continued to throng sights such as the city’s main square. “It is reassuring to see the police. We are concerned but not frightened,” said Emilio Bravo, who had travelled to Brussels from Alicante, Spain.

However, the Sunday morning market at the city’s Eurostar terminal Gare du Midi – one of the biggest outdoor markets in Europe – was called off. Busy trains from Paris were subject to extra security measures.

Belgian officials have said that they are hunting at least two men. One is 26-year-old Abdeslam. The Belgian interior minister, Jan Jambon, said “several suspects” tied to the Paris attacks could be at large in the country, amid speculation that a series of cells may be planning further strikes in the heart of the EU. A meeting of security agencies and senior ministers was held on Sunday afternoon to decide whether the metro will be allowed to function on Monday morning.

Other measures may be relaxed, or stiffened, depending on inputs from counter terrorist agencies, officials said. “We are clearly dealing with intelligent individuals who can change their targets and tactics depending on what we do ... So all this could take a certain time, that’s obvious,” Koen Geens, the justice minister, told a local TV network.

Many in Belgian’s Muslim community, which numbers around 600,000, fear a backlash as tensions continue.

“We are very happy to see the searches and hear about the arrests,” said Dekhili Marouan, a 35-year-old catering worker who arrived in Belgium from Tunisia five years ago. “It’s frightening for everybody. I’m worried too about people here blaming all of us Muslims for this. These people who do this kind of violence, they are not Muslims.”

Belgian officials have rejected widespread criticism of the country’s intelligence services and counter-terror efforts. But the news that a Belgian man suspected of undertaking reconnaissance for the Paris attacks’ targets has been held by Turkish police has underlined the country’s role as a base for those behind the plot.

The US embassy in Brussels advised Americans to cancel their weekend plans and stay indoors. The Foreign Office delivered similar advice for the high numbers of Britons in Brussels, which is also home to the Nato headquarters.

Geens, the justice minister, said that the Paris attacks had shown that the profile of potential targets had changed. “It’s no longer synagogues or the Jewish museums or police stations, it’s mass gatherings and public places,” he said.

Three days of the highest terror alert and unprecedented measures that have closed down the city’s subways, schools and main stores, has created a very different atmosphere as the Belgian capital tries to avoid attacks similar to the ones that caused devastating carnage in Paris.